1. Field of the Invention
This invention concerns fabrication of molded shapes and more particularly apparatus for manufacturing shell molds which is adapted to automated manufacturing operations.
2. Description of the Prior Art
The shell mold process for the production of foundry molds is widely utilized in industry since it has many marked advantages over the older green sand molding process, such as the ease of obtaining close tolerance castings with excellent surface finish, good and consistent pattern reproduction, the quantity of sand is reduced, the molds may be stored indefinitely, etc. The fabrication of the shell mold basically involves the use of a molding mix comprised of a dry mixture of sand and a thermosetting resin, the thermosetting resins either mixed thereinto as a separate granulation from the dry sand or, as more recently practiced, the sand grains themselves may be coated with the resin to insure uniformity of dispersion of the resin and sand. The process includes the step of preheating a mold pattern prior to dispensing a quantity of the mixture onto the pattern, where it is allowed to remain for a short interval. The excess which does not adhere to the pattern is then discharged, and the mold pattern is placed in a curing oven to thoroughly cure the resin binder and form a relatively thin but strong mold which is then removed from the pattern ready for use.
The relative simplicity of the shell molding process lends itself to being automated and many such arrangements are known in the prior art. However, these approaches usually involve relatively complicated rotary transfer or conveyor means for transporting the pattern through the various stations where the necessary operations for carrying out the fabrication of the shell mold are performed, with relatively complicated controls required to synchronize the various operations with the transport of the pattern.
Furthermore, numerous solenoid or fluid pressure actuators for carrying out the various operations are required, which actuators in some designs are subjected to heating in the curing or pattern preheating ovens. These factors lead to considerable maintenance requirements for the machinery involved and also to a none-too-reliable performance.
In addition, the conventional practice in which separate ovens for preheating the pattern and for curing the mold is relatively wasteful of energy, and if both heating functions could be carried out by a single oven, a more energy efficient process would result.
In connection with this latter point, oven closures have commonly been dispensed with since the required automatic controls would further increase the complexity and accordingly the maintenance requirements of the apparatus, further exacerbating the energy wastefulness of the equipment.
It is therefore an object of the present invention to provide a process and apparatus for production of molded shapes such as shell molds adapted to automated manufacture thereof by means of a simplified transport mechanism and associated controls.
It is a further objection of the present invention to provide such an arrangement in which the number of actuator devices is greatly reduced.
It is yet another object of the present invention to provide such a system in which a single oven can provide both the pattern heating and mold curing functions.